The purpose of the project is to achieve an understanding of the interaction of follitropin (FSH) with hormone specific receptors of testes. Highly purified FSH, radioiodinated under conditions permitting retention of biological activity and further purified by target tissue affinity chromatography will be utilized as the ligand in these studies. Wherever possible, homologous hormone-receptor systems will be employed. A comparison will be made of the properties of FSH receptors present in tubule plasma membranes with solubilized and purified FSH receptors. Solubilization of the FSH receptor will initially be done through use of Triton X-100, but different detergents and other media such as chaotropic agents and organic solvents will be studied in an attempt to improve the process. Polyethylene glycol precipitation will be employed for separation for 125I-FSH bound to soluble receptor from unbound hormone, but improvements in this procedure will also be investigated. Purification of solubilized FSH receptors will be mainly from calf or bull testis. A variety of approaches will be used, but it is hoped that affinity chromatography will allow a rapid advance in this area. A careful kinetic and thermodynamic analysis of interaction between FSH and particulate and purified solubilized receptors will be undertaken. Structure-function relationships of hormone and receptor will be probed through use of chemical and enzymic modifications of either or both. Antiserum will be raised against the purified receptor with a view to development of a radioimmunoassay for its measurement as well as for use in studies of receptor physiology. We will attempt to develop a hormonally sensitive, solubilized receptor-adenylate cyclase system to allow a precise study of mechanism leading to enzyme activation and cAMP formation. The nature and properties of testicular and serum factors which inhibit uptake of 125I-FSH by its receptors will be intensively studied and efforts will be made to ascertain their physiologic relevance and potential application in contraception.